Solid electrolytic capacitors and method for manufacturing the same

ABSTRACT

A solid electrolytic capacitor of the present invention comprises an positive electrode body, a dielectric layer disposed on the surface of the positive electrode body, a solid electrolyte layer disposed on the surface of the dielectric layer, a negative electrode layer disposed on the surface of the solid electrolyte layer, an positive electrode terminal electrically connected to the positive electrode body, and a negative electrode terminal electrically connected to the negative electrode layer, wherein the negative electrode layer includes a carbon layer and a conductor layer, and the carbon layer contains carbon particles and a benzene compound shown by the chemical formula 1. The whole is covered with facing resin while exposing the positive electrode terminal led out of the positive electrode body and the negative electrode terminal led out of the negative electrode layer. With this configuration, the carbon layer formed is fine and uniform. Accordingly, the contact resistance between the solid electrolyte layer and the carbon layer is reduced, and the contact resistance between the carbon layer and the conductor layer. As a result, it is possible to obtain a solid electrolytic capacitor assuring excellent equivalent series resistance characteristic and capacity utilization factor.  
     Chemical formula 1  
     where each of R1, R2, R3, and R4 has H, OH group, COOH group, or alkyl group.

FIELD OF THE INVENTION

[0001] The present invention relates to solid electrolytic capacitorsusing solid electrolyte and a method for manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] Due to the remarkable development of digital equipment in recentyears, there is a strong demand for capacitors having high frequencycharacteristics, which are of low impedance even in a high frequencyrange. As capacitors available to meet such demand of the market,capacitors using solid electrolyte layers such as manganese dioxide,polypyrrole or polythiophene are known.

[0003]FIG. 3 is a sectional view showing the configuration of aconventional solid electrolytic capacitor. In FIG. 3, a dielectric oxidefilm 33 formed by an positive electrode oxidation method is disposed onthe surface of an positive electrode body 32. The positive electrodebody 32 is enclosed in the dielectric oxide film 33. The positiveelectrode body 32 is made by sintering valve metal such as aluminum andtitanium into porous metal. Positive electrode lead wire 31 is connectedto the positive electrode body 32, and a part of the positive electrodelead wire 31 is outwardly led from the surface of the dielectric oxidefilm 33.

[0004] A solid electrolyte layer 34 such as manganese or polypyrrole isdisposed on the surface of the positive electrode body 32 having thedielectric oxide film 33, and a negative electrode layer 35 comprising acarbon layer and a conductor layer is disposed on the solid electrolytelayer 34. A capacitor element 36 is formed in this way. An positiveelectrode terminal 37 is connected to the positive electrode lead wire31 of a capacitor element 36. A negative electrode terminal 39 isconnected to the negative electrode layer 35 via conductive adhesive 38.Facing resin 40 being electrically insulative is disposed so as to coverthe capacitor element 36. The positive electrode terminal 37 and thenegative electrode terminal 39 are partially exposed to the outside. Thesolid electrolytic capacitor is configured in this way.

[0005] In such conventional solid electrolytic capacitor, the solidelectrolyte layer 34 is extremely low in resistibility, and it has beenable to reduce the equivalent series resistance (hereinafter called ESRcharacteristic) of the solid electrolytic capacitor.

[0006] However, in a conventional solid electrolytic capacitor asmentioned above, in case the oxide of transition metal such as manganesedioxide, or solid electrolyte layer 34 contains a conductive polymercomprising heterocyclic compound such as polypyrrole, and in case acarbon layer is formed on the solid electrolyte layer 34 by use ofaqueous solution including carbon particles and coagulation stabilizer,it will sometimes cause generation of uneven carbon layers or thin filmportions because the surface tension of the aqueous solution is toohigh. Therefore, it has been extremely difficult to form uniform carbonlayers.

[0007] Accordingly, lots of defective products have been generated withrespect to ESR characteristic and capacity utilization factor, and as aresult, there has been a problem of lowering in yield of the products.

[0008] The present invention provides a solid electrolytic capacitorassuring excellent ESR characteristic and capacity utilization factor,which has been reduced in contact resistance between the solidelectrolyte layer and negative electrode layer, and a method formanufacturing same.

SUMMARY OF THE INVENTION

[0009] A solid electrolytic capacitor in accordance with the presentinvention comprises

[0010] an positive electrode body,

[0011] a dielectric layer formed on the surface of the positiveelectrode body,

[0012] a solid electrolyte layer formed on the surface of the dielectriclayer,

[0013] a negative electrode layer disposed on the surface of the solidelectrolyte layer,

[0014] an positive electrode terminal electrically connected to thepositive electrode body, and

[0015] a negative electrode terminal electrically connected to thenegative electrode layer,

[0016] wherein the negative electrode layer includes a carbon layer, and

[0017] the carbon layer contains carbon particles, and a benzenecompound represented by chemical formula 1.

Chemical formula 1

[0018] where each of R1, R2, R3, and R4 has H, OH group, COOH group, oralkyl group.

[0019] Preferably, the positive electrode body includes valve metal, andthe dielectric layer includes a dielectric oxide film formed byoxidation of the valve metal.

[0020] Preferably, the negative electrode layer further includes aconductor layer, a carbon layer is disposed on the surface of thedielectric layer, and the conductor layer is disposed on the surface ofthe carbon layer.

[0021] Preferably, the positive electrode body includes valve metal; thedielectric layer includes a dielectric oxide film formed by oxidation ofthe valve metal; the negative electrode layer further includes aconductor layer; a carbon layer is disposed on the surface of thedielectric oxide film; and the conductor layer is disposed on thesurface of the carbon layer.

[0022] Preferably, the solid electrolytic capacitor further comprisesfacing resin; each of the positive electrode terminal and the negativeelectrode terminal is partially exposed; and the facing resin isdisposed so as to cover the positive electrode body, the dielectriclayer, the solid electrolyte layer, and the negative electrode layer.

[0023] Due to this configuration, the carbon layer formed is fine anduniform. Accordingly, the contact resistance between the solidelectrolyte layer and the carbon layer will be reduced. Further, thecontact resistance between the carbon layer and the conductor layer willalso be reduced. As a result, it is possible to obtain a solidelectrolytic capacitor assuring excellent ESR characteristic andcapacity utilization factor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a sectional view showing the configuration of a solidelectrolytic capacitor in accordance with the exemplary embodiment 1 andthe exemplary embodiment 2 of the present invention.

[0025]FIG. 2 is a perspective view showing the configuration partiallybroken away of a solid electrolytic capacitor in accordance with theexemplary embodiment 3 of the present invention.

[0026]FIG. 3 is a sectional view showing the configuration of aconventional solid electrolytic capacitor.

DESCRIPTION OF THE MARKS

[0027] 1 Positive electrode lead wire

[0028] 2 Positive electrode body

[0029] 3 Dielectric oxide film

[0030] 4 Solid electrolyte layer

[0031] 5 Carbon layer

[0032] 6 Silver paste conductor layer

[0033] 7 Capacitor element

[0034] 8 Positive electrode terminal

[0035] 9 Conductive adhesive

[0036] 10 Negative electrode terminal

[0037] 11 Facing resin

DETAILED DESCRIPTION OF THE INVENTION

[0038] In a solid electrolytic capacitor and its manufacturing method ofthe present invention, a carbon layer serves to relieve the surfacetension generated when a carbon layer is formed.

[0039] That is, a solid electrolytic capacitor in an embodiment of thepresent invention comprises an positive electrode body formed of valvemetal; a dielectric oxide film, a solid electrolyte layer and a negativeelectrode layer which are laminated in order on the surface of thepositive electrode body; electrically insulative resin as a facingdisposed so as to cover these laminated layers; an positive electrodeterminal led out of the positive electrode body; and a negativeelectrode terminal led out of the negative electrode layer. Each of thepositive electrode terminal and the negative electrode terminal ispartially exposed at the surface of the resin. The negative electrodelayer includes a carbon layer and a conductor layer. The carbon layercontains carbon particles and a benzene compound represented by thechemical formula 1. Due to this configuration, the carbon layer formedis fine and uniform. Accordingly, the contact resistance between thesolid electrolyte layer and the carbon layer will be reduced. Further,the contact resistance between the carbon layer and the conductive layerwill also be reduced. As a result, it is possible to obtain a solidelectrolytic capacitor assuring excellent ESR characteristic andcapacity utilization factor.

Chemical formula 1

[0040] where each of R1, R2, R3, and R4 has H, OH group, COOH group, oralkyl group.

[0041] Preferably, the carbon particles, and the benzene compoundrepresented by the chemical formula 1 are contained at a ratio of onepart by weight of carbon particles and 0.1˜1.8 part by weight of benzenecompound represented by the chemical formula 1. With this configuration,the carbon layer formed is fine and uniform.

[0042] Preferably, the benzene compound represented by the chemicalformula 1 which is included in the carbon layer contains catechol orpyrogallol. As pyrogallol, for example, a benzene compound having C₆H₆O₃as shown by the chemical formula 2 is used. As catechol, for example, abenzene compound having C₆H₆O₂ as shown by the chemical formula 3 isused.

[0043] A method for manufacturing a solid electrolytic capacitor in anembodiment of the present invention comprises

[0044] (a) a process of forming a dielectric oxide film and a solidelectrolyte layer in order on the surface of an positive electrode bodyformed by sintering valve metal into porous metal or on the surface ofan positive electrode body with the foil of valve metalsurface-roughened;

[0045] (b) a process of forming a negative electrode layer by forming acarbon layer containing carbon particles and a benzene compoundrepresented by the chemical formula 1 and a conductive layer of silverpaste on the surface of the solid electrolyte layer; and

[0046] (c) after that, a process of facing the whole with resin in amanner such that each of an positive electrode terminal led out of thepositive electrode body and a negative electrode terminal led out of thenegative electrode layer is partially exposed.

[0047] According to this method, it is possible to reliably obtain asolid electrolyte capacitor assuring excellent ESR characteristic andcapacity utilization factor.

[0048] Exemplary embodiment 1:

[0049]FIG. 1 is a sectional view showing the configuration of a solidelectrolyte capacitor in accordance with the exemplary embodiment 1 ofthe present invention. In FIG. 1, the solid electrolyte capacitorcomprises an positive electrode 2 formed of valve metal; a dielectricoxide film 3, a solid electrolyte layer 4 and a negative electrode layerwhich are laminated in order on the surface of the positive electrodebody 2; facing resin 11 disposed so as to cover these laminated layers;positive electrode lead wire 1 led out of the positive electrode body 2;an positive electrode terminal 8 connected to the positive electrodelead wire 1; and a negative electrode terminal 10 led out of thenegative electrode layer.

[0050] Each of the positive electrode terminal 8 and the negativeelectrode terminal 10 is partially exposed at the surface of the facingresin 11. The solid electrolyte layer 4 contains manganese dioxide. Asvalve metal, aluminum and titanium or the like metal are used, and thesemetals are sintered into porous metals. The dielectric oxide film 3 isformed by an positive electrode oxidation method. The negative electrodelayer includes a carbon layer 5 and a silver paste conductor layer 6.The negative electrode terminal 10 is connected to the negativeelectrode layer via a conductive adhesive 9.

[0051] The carbon layer 5 contains carbon particles and a benzenecompound represented by the chemical formula 1.

[0052] The configuration mechanism of carbon particles and a benzenecompound shown by the chemical formula 1 is unknown. However, the carbonlayer 5 obtained is fine and uniform because of containing both ofcarbon particles and a benzene compound shown by the chemical formula 1.Accordingly, the contact resistance between the solid electrolyte layer4 and the carbon layer 5 will be reduced.

[0053] The carbon layer 5 contains a benzene compound shown by thechemical formula 1 in a range of 0.1 to 1.8 part by weight of sameagainst one part by weight of carbon particles. Since the carbon layer 5has such a range of chemical composition, the carbon layer 5 obtained isfine and uniform. Accordingly, the contact resistance between the solidelectrolyte layer 4 and the carbon layer 5 will be reduced. Favorably,the carbon layer 5 contains a benzene compound shown by the chemicalformula 1 in a range of 0.2 to 1.2 part by weight of same against onepart by weight of carbon particles. Due to this configuration, theresult to be obtained will be further improved.

[0054] In case the content of the benzene compound represented by thechemical formula 1 is less than 0.1 part by weight, a uniform carbonlayer will not be obtained. Also, the content of the benzene compoundrepresented by the chemical formula 1 exceeds 1.8 part by weight, thecarbon layer formed will be thick and not uniform, and it is unable toobtain a uniform layer.

[0055] As a benzene compound shown by the chemical formula 1, at leastone of catechol and pyrogallot is preferable in particular. Thesecompounds may relieve the surface tension that becomes extremely highduring forming of a carbon layer. Accordingly, the contact resistancebetween the solid electrolyte layer and the carbon layer will bereduced. As a result, it is possible to obtain a solid electrolyticcapacitor having excellent ESR characteristic in a high frequency range.

[0056] The carbon layer 5 is formed through processes such as, a processof preparing an alkaline (pH8˜11) mixture or solution suspended byadding carbon particles of submicron in diameter, a benzene compoundrepresented by the chemical formula 1, and a surface active agent intowater, and a process of applying the alkaline mixture to the surface ofsolid electrolyte layer 4 and drying of same.

[0057] Or, a process of forming the carbon layer includes:

[0058] (a) a step of preparing a suspension of carbon particles andliquid;

[0059] (b) a step of preparing a mixed suspension by dissolving abenzene compound shown by the chemical formula 1 in the suspension;

[0060] (c) a step of immersing the positive electrode body having thesolid electrolyte layer into the mixed suspension;

[0061] (d) a step of taking the positive electrode body having theelectrolyte layer out of the mixed suspension; and

[0062] (e) a step of drying the positive electrode body having the solidelectrolyte layer, which is moistened with the mixed suspension.

[0063] Because the mixture (or solution) is alkaline, the dispersion ofcarbon particles will be improved. Accordingly, it is possible toincrease the stability of the benzene compound represented by thechemical formula 1. In case the mixture (or solution) is acidic (interms of pH), the dispersion of carbon particles becomes worse, andconsequently, the benzene compound will be lowered in stability.

[0064] The content of carbon particles in the mixture (or solution) ispreferable to be in a range from 2 wt % to 10 wt %. In this way, thedispersion of carbon particles will be further improved. As a result,the carbon layer 5 obtained is fine and uniform. When the content ofcarbon particles in the mixture (or solution) is less than 2 wt % orover 10 wt %, the above performance will be lowered a little.

[0065] Specific examples are described in the following.

EXAMPLE 1

[0066] Firstly, tantalum powder is molded in a manner such that a partof tantalum wire is exposed. After that, the moldings is sintered. Inthis way, an positive electrode body of 1.4 mm in thickness, 3.0 mm inwidth, and 3.8 mm in length was obtained. The surface of the positiveelectrode body is subjected to formation at 20V by using phosphatesolution. Thus, a dielectric oxide film was formed as a dielectriclayer. A lead wire is connected to the positive electrode body and isled out of the positive electrode body.

[0067] Next, the positive electrode body having the dielectric oxidefilm was immersed into 20 wt % of manganese nitrate solution at 25° C.for 10 seconds, and was taken out thereafter. After that, excess part ofthe manganese nitrate solution sticking to the surface of the positiveelectrode body having the dielectric oxide film was blown away by air.Subsequently, the positive electrode body moistened with manganesenitrate solution was treated at 300° C. for 5 minutes, increasing thetemperature at a speed of over 250° C. within one minute. Thus, themanganese nitrate solution was thermally decomposed and then a solidelectrolyte layer of manganese dioxide was formed on the surface of thedielectric oxide film.

[0068] Next, the surface of the solid electrolyte layer was impregnatedwith alkaline solution containing carbon particles and pyrogallol.Pyrogallol is used as a benzene compound shown by the chemicalformula 1. The alkaline solution contains 2 wt % of carbon particles and2 wt % of pyrogallol, and ammonia. The solution is adjusted to pH10 byammonia. The positive electrode body impregnated with the alkalinesolution was dried at 150° C. In this way, a carbon layer was formed onthe surface of the solid electrolyte layer. After that, a silver pastewas formed as a conductive layer on the surface of the carbon layer.Thus, a capacitor element was obtained.

[0069] Next, a positive electrode terminal was connected to a tantalumwire. Also, a negative electrode terminal is connected to a negativeelectrode layer by using conductive adhesive. That is, the negativeelectrode terminal is connected to the negative electrode layer via theconductive adhesive. Facing resin is disposed to cover the capacitorelement in a manner such that each of the positive electrode terminaland the negative electrode terminal is partially exposed. In this way, asolid electrolytic capacitor having a shape of 7.3 mm×4.3 mm×2.8 mm indimension was manufactured.

EXAMPLE 2

[0070] In this example 2, a carbon layer is formed by using alkalinesolution containing carbon particles and catechol as a benzene compoundshown by the chemical formula 1. The other configurations to obtain asolid electrolytic capacitor are the same as in the above example 1.

EXAMPLE 3

[0071] In this example 3, a carbon layer is formed by using alkalinesolution of pH10 which contains 5 wt % of carbon particles and 0.5 wt %of pyrogallol. In this case, the carbon layer contains one part byweight of carbon particles and 0.1 part by weight of pyrogallol. Theother configurations to obtain a solid electrolytic capacitor are thesame as in the above example 1.

EXAMPLE 4

[0072] In this example 4, a carbon layer is formed by using alkalinesolution of pH10 which contains 5 wt % of carbon particles and 2 wt % ofpyrogallol. In this case, the carbon layer contains one part by weightof carbon particles and 0.4 part by weight of pyrogallol. The otherconfigurations to obtain a solid electrolytic capacitor are the same asin the above example 1.

EXAMPLE 5

[0073] In this example 5, a carbon layer is formed by using alkalinesolution of pH10 which contains 5 wt % of carbon particles and 5 wt % ofpyrogallol. In this case, the carbon layer contains one part by weightof carbon particles and 1.0 part by weight of pyrogallol. The otherconfigurations to obtain a solid electrolytic capacitor are the same asin the above example 1.

EXAMPLE 6

[0074] In this example 6, a carbon layer is formed by using alkalinesolution of pH10 which contains 5 wt % of carbon particles and 6 wt % ofpyrogallol. In this case, the carbon layer contains one part by weightof carbon particles and 1.2 part by weight of pyrogallol. The otherconfigurations to obtain a solid electrolytic capacitor are the same asin the above example 1.

EXAMPLE 7

[0075] In this example 7, a carbon layer is formed by using alkalinesolution of pH10 which contains 5 wt % of carbon particles and 9 wt % ofpyrogallol. In this case, the carbon layer contains one part by weightof carbon particles and 1.8 part by weight of pyrogallol. The otherconfigurations to obtain a solid electrolytic capacitor are the same asin the above example 1.

EXAMPLE 8

[0076] In this example 8, a carbon layer is formed by using alkalinesolution of pH10 which contains 10 wt % of carbon particles and 10 wt %of pyrogallol. In this case, the carbon layer contains one part byweight of carbon particles and 1.0 part by weight of pyrogallol. Theother configurations to obtain a solid electrolytic capacitor are thesame as in the above example 1.

Comparative example 1

[0077] In this comparative example 1, a carbon layer is formed by usingalkaline solution of pH10 which contains 2 wt % of carbon particles.That is, the alkaline solution does not contain a benzene compound shownby the chemical formula 1. The other configurations to obtain a solidelectrolytic capacitor are the same as in the above example 1.

Comparative example 2

[0078] In this comparative example 2, a carbon layer is formed by usingalkaline solution of pH10 which contains 5 wt % of carbon particles.That is, the alkaline solution does not contain a benzene compound shownby the chemical formula 1. The other configurations to obtain a solidelectrolytic capacitor are the same as in the above example 1.

[0079] With respect to the solid electrolytic capacitors thus obtainedin the examples 1 to 8 and the comparative examples 1 and 2, the initialcharacteristics (electrostatic capacity “C”, equivalent seriesresistance “ESR”, leak current “LC”), capacity change rate “ΔC” and ESRchange rate “ΔESR” after 1,000 hours of leaving at 105° C. are shown inTable 1. These performances were measured at temperatures in a range of25˜30° C. The electrostatic capacity was measured at 120 Hz. ESR wasmeasured at 100 kHz. As the leak current, the current value was measured30 seconds after applying the rated voltage. Each of the measured valuesis shown by averaging n=30 specimens. The rated specification of thesolid electrolytic capacitor is 6.3WV, 150 μF. TABLE 1 Initial valuesAfter 1,000 hours C (μF) ESR (mΩ) LC (μA) ΔC (%) ΔESR (%) Example 1 15230 15 −2.5 1.5 Example 2 154 28 14 −2.1 1.3 Example 3 150 24 13 −2.0 1.2Example 4 153 22 11 −1.8 0.9 Example 5 154 21 10 −1.7 0.8 Example 6 15923 12 −1.8 0.9 Example 7 156 25 13 −2.2 1.3 Example 8 155 24 13 −2.1 1.2Comparative 121 75 94 −15 17 example 1 Comparative 126 72 82 −12 11example 2

[0080] As shown in Table 1, the solid electrolytic capacitors in theexample 1 and the example 2, containing carbon particles and pyrogallolor catechol in the carbon layer, have better initial characteristicsthan those in the comparative examples. Further, the solid electrolyticcapacitors in the present examples maintain excellent performance evenafter 1,000 hours of leaving at high temperatures. That is, in thepresent examples, the electrostatic capacity is 152-154 μF, ESR is 28-30mΩ, and leak current is 14-15 μA. Also, after 1,000 hours of leaving at105° C., the capacity change rate (ΔC) is 2.1˜2.5%, and ESR change rateis 1.3-1.5%. On the other hand, in the comparative example 1, theelectrostatic capacity is 121 μF, ESR is 75 mΩ or less, and leak currentis 94 μA. Furthermore, after 1,000 hours of leaving at 105° C., thecapacity change rate (ΔC) is 15%, and ESR change rate is 17%.

[0081] Also, the solid electrolytic capacitors in the examples 3 to 8show the characteristics of a solid electrolytic capacitor which can beobtained by changing the content of pyrogallol in the carbon layerforming process. Because the carbon layer contains 0.2 part to 1.8 partby weight of pyrogallol against one part by weight of carbon particles,the initial characteristics obtained are better than those in thecomparative example 2. Further, the solid electrolytic capacitors in thepresent examples maintain excellent performance even after 1,000 hoursof leaving at high temperatures. That is, the electrostatic capacity is150-159 μF, ESR is 21-25 mΩ, and leakcurrent is 10-13 μA or less. Also,after 1,000 hours of leaving at 105° C., the capacity change rate (ΔC)is 1.7-2.1%, and ESR change rate is 0.8-1.3%. On the other hand, in thecomparative example 2, the electrostatic capacity is 126 μF, ESR is 72mΩ or less, and leak current is 82 μA. Furthermore, after 1,000 hours ofleaving at 105° C., the capacity change rate (ΔC) is 12%, and ESR changerate is 11%.

[0082] Thus, the solid electrolytic capacitors in the present examplesare 150 μF or over in electrostatic capacity, 35 mΩ or less in ESR, and20 μA or less in leak current. Furthermore, the solid electrolyticcapacitors in the present examples are, after 1,000 hours of leaving at105° C., within 3% in capacity change rate (ΔC) and within 2% in ESRchange rate. On the other hand, the solid electrolytic capacitors in thecomparative examples are 126 μF or less in electrostatic capacity, 72 mΩor over in ESR, and 82 μA or over in leak current. Further, the solidelectrolytic capacitors in the comparative examples, after 1,000 hoursof leaving at 105° C., are 12% or over in capacity change rate (ΔC) and11% or over in ESR change rate.

[0083] Exemplary embodiment 2:

[0084] In the exemplary embodiment 2, a solid electrolyte layer isformed of a conductive polymer. The other configurations to obtain asolid electrolytic capacitor are the same as in the above exemplaryembodiment 1.

[0085] As a conductive polymer, it is preferable to use a heterocyclicpolymer such as polypyrrole, polythiophene, polyaniline, or poly-3,4-ethylene dioxythiophene.

[0086] These conductive polymers are formed through chemical oxidativepolymerization of heterocyclic monomers.

[0087] The first method of forming solid electrolyte layer 4 ofconductive polymer comprises (a) a process of impregnating the surfaceof dielectric oxide film 3, formed on the surface of positive electrodebody 2, with a polymerizing solution containing a heterocylic monomer,and further, impregnating same with an oxidizing solution containing anoxidizing agent, followed by cleaning and recovery formation; and (b) aprocess of repeating the process (a) by a plurality of times.

[0088] The second method of forming solid electrolyte layer 4 ofconductive polymer comprises (c) a process of impregnating the surfaceof dielectric oxide film 3, formed on the surface of positive electrodebody 2, with a mixed solution containing a heterocyclic monomer and anoxidizing agent, and (d) a process of repeating the process (c) by aplurality of times.

[0089] The third method of forming solid electrolyte layer 4 ofconductive polymer comprises (e) a process of impregnating the surfaceof dielectric oxide film 3, formed on the surface of positive electrodebody 2, with a polymerizing solution containing a heterocylic monomer,and further, impregnating same with an oxidizing solution containing anoxidizing agent, and further, with a mixed solution containing aheterocyclic monomer and an oxidizing agent, followed by cleaning andrecovery formation; and (f) a process of repeating the process (e) by aplurality of times.

[0090] As a heterocyclic monomer, it is preferable to use a monomer suchas pyrrole, thiophene, aniline, or 3, 4-ethylen dioxythiophene. Solidelectrolyte layer 4 of conductive polymer having a relatively highconductivity can be obtained through chemical oxidative polymerizationof these hetercyclic monomers.

[0091] Also, as oxidizing agents, for example, ferric salt, persulfate,permanganate, and hydrogen peroxide are employed. It is preferable touse iron sulfate or ferric p-toluene sulfonate as an oxidizing agent.

[0092] The examples in the exemplary embodiment 2 will be described inthe following.

EXAMPLE 21

[0093] Firstly, tantalum powder is molded in a manner such that a partof tantalum wire is exposed. After that, the moldings is sintered. Inthis way, an positive electrode body of 1.4 mm in thickness, 3.0 mm inwidth, and 3.8 mm in length was obtained. The surface of the positiveelectrode body is subjected to formation at 20V by using phosphatesolution. Thus, a dielectric oxide film was formed as a dielectriclayer. The lead wire is connected to the positive electrode body and isexposed at the surface of the dielectric oxide film.

[0094] Next, the positive electrode body having the dielectric oxidefilm was immersed in a polymerizing solution containing a heterocyclicmonomer for 5 minutes, and taken out thereafter. The polymerizingsolution contains ethylene glycol solution, sodium alkyl naphthalenesulfonate, and heterocyclic monomer. Pyrrole is used as a heterocyclicmonomer. After that, the positive electrode body having the dielectricoxide film is immediately immersed in an oxidizing solution including anoxidizing agent for 10 minutes, and taken out thereafter. The oxidizingsolution contains ethylene glycol solution and ferrous sulfate (III).The positive electrode body was cleaned and then subjected to recoveryformation, followed by drying at 100° C. A series of these operationswere repeated 10 times. In this way, a conductive polymer as a solidelectrolyte layer was formed on the surface of the positive electrodebody.

[0095] Next, the surface of the solid electrolyte layer was impregnatedwith alkaline solution containing carbon particles and pyrogallol.Pyrogallol contains a benzene compound of chemical formula 1. Thealkaline solution contains 2 wt % of carbon particles and 2 wt % ofpyrogallol, and ammonia. The solution is adjusted to pH10 by ammonia.The positive electrode body impregnated with the alkaline solution wasdried at 150° C. In this way, a carbon layer was formed on the surfaceof the solid electrolyte layer. After that, a silver paste conductorlayer was formed on the surface of the carbon layer. Thus, a capacitorelement was obtained.

[0096] Next, a positive electrode terminal was connected to a tantalumwire. Also, a negative electrode terminal was connected to a negativeelectrode layer by using conductive adhesive. That is, the negativeelectrode terminal is connected to the negative electrode layer via theconductive adhesive. Facing resin is disposed to cover the capacitorelement in a manner such that each of the positive electrode terminaland the negative electrode terminal is partially exposed. In this way, asolid electrolytic capacitor having a shape of 7.3 mm×4.3 mm×2.8 mm indimension was manufactured.

EXAMPLE 22

[0097] In the example 22, the solid electrolyte layer is formed by usinga polymerizing solution containing thiophene as a heterocyclic monomer.That is, the solid electrolyte layer contains polythiophene formedthrough polymerization of thiophene. The other configurations to obtaina solid electrolytic capacitor are the same as in the above example 21.

EXAMPLE 23

[0098] In this example 23, a solid electrolyte layer is formed by usinga polymerizing solution containing aniline as a heterocyclic monomer.That is, the solid electrolyte layer contains polyaniline formed throughpolymerization of aniline. The other configurations to obtain a solidelectrolytic capacitor are the same as in the above example 21.

EXAMPLE 24

[0099] In this example 24, a solid electrolyte layer is formed by usinga polymerizing solution containing 3. 4-ethylene dioxythiophene as aheterocyclic monomer. That is, the solid electrolyte layer containspoly-3, 4-ethylene dioxythiophene formed through polymerization of 3,4-ethylene dioxythiophene. The other configurations to obtain a solidelectrolytic capacitor are the same as in the above example 21.

Comparative example 3

[0100] In this comparative example 3, a carbon layer is formed by usingalkaline solution of pH10 which contains 2 wt % of carbon particles.That is, the alkaline solution does not contain a benzene compoundrepresented by the chemical formula 1. The other configurations toobtain a solid electrolytic capacitor are the same as in the aboveexample 21.

[0101] With respect to the solid electrolytic capacitors thus obtainedin the examples 21˜24 and the comparative examples 3, the initialcharacteristics (electrostatic capacity “C”, equivalent seriesresistance “ESR”, leak current “LC”), capacity change rate “ΔC” and ESRchange rate “ΔESR” after 1,000 hours of leaving at 105° C. are shown inTable 2. These performances were measured at temperatures in a range of25˜30° C. The electrostatic capacity was measured at 120 Hz. ESR wasmeasured at 100 kHz. As the leak current, the current value was measured30 seconds after applying the rated voltage. Each of the measured valuesis shown by averaging n=30 specimens. Here, the rating of the solidelectrolytic capacitor is 6.3WV, 150 μF. TABLE 2 Initial values After1,000 hours C (μF) ESR (mΩ) LC (μA) ΔC (%) ΔESR (%) Example 21 152 20 11−1.8 1.0 Example 22 154 21 10 −1.9 1.1 Example 23 153 20 11 −1.8 1.1Example 24 158 18 9 −1.6 0.8 Comparative 126 82 82 −11 12 example 3

[0102] As shown in Table 2, the solid electrolytic capacitors in theexamples 21 to 24, containing carbon particles and pyrogallol orcatechol in the carbon layer, have better initial characteristics thanthose in the comparative example. Further, the solid electrolyticcapacitors in the present examples maintain excellent performance evenafter 1,000 hours of leaving at high temperatures. That is, in thepresent examples, the electrostatic capacity is 152-158 μF, ESR is 18-21mΩ, and leak current is 9-11 μA. Also, after 1,000 hours of leaving at105° C., the capacity change rate (ΔC) is 1.6-1.8%, and ESR change rateis 0.8-1.1%. On the other hand, in the comparative example 3, theelectrostatic capacity is 126 μF, ESR is 82 mΩ or less, and leak currentis 82 μA. Furthermore, after 1,000 hours of leaving at 105° C., thecapacity change rate (ΔC) is 11%, and ESR change rate is 12%.

[0103] Thus, the solid electrolyte capacitors in the examples 21 to 24have better initial characteristics than those in the comparativeexample, and are also lower in capacity change rate and ESR change rateafter 1,000 hours of leaving at 105° as compared with the comparativeexample.

[0104] Exemplary embodiment 3:

[0105]FIG. 2 is a perspective view, partially broken away, showing theconfiguration of a solid electrolytic capacitor in the exemplaryembodiment 3 of the present invention. In FIG. 2, the solid electrolyticcapacitor comprises an positive electrode body 21 having a dielectricoxide film 22, a manganese dioxide layer 23, a solid electrolyte layer24, a negative electrode layer 25, an insulation resist 20, terminalmember 26A, 26B, and facing resin 27.

[0106] The positive electrode body 21 is formed of aluminum foil asvalve metal, and the positive electrode body is rough-surfaced. Thealuminum foil surface is rough-surfaced by etching. After that, therough surface of the aluminum foil is subjected to formation, and adielectric oxide film 22 is formed on the aluminum foil surface. Theinsulation resist 20 is disposed to separate the aluminum foil into anpositive electrode portion and a negative electrode portion. That is,the aluminum foil is separated into an positive electrode portion and anegative electrode portion by the insulation resist 20. Manganesedioxide layer 23 and solid electrolyte layer 24 are formed on thenegative electrode portion of the aluminum foil. That is, the negativeelectrode portion includes the manganese dioxide layer 23 and the solidelectrolyte layer 24. As solid electrolyte layer 24, a conductivepolymer such as polypyrrole, polythiophene or polyaniline is employed.The negative electrode layer 25 is arranged over the solid electrolytelayer 24. The negative electrode layer 25 includes a carbon layer, andsilver paste as a conductor layer. A capacitor element is configured inthis way. Using a single or a plurality of such capacitor elementslaminated, the terminal member 26A is connected to the positiveelectrode portion, and the terminal member 26B is connected to thenegative electrode portion. After that, the facing resin 27 is molded soas to cover the capacitor element. Thus, a solid electrolytic capacitoris formed.

[0107] The manganese dioxide layer 23 is formed through a process ofimpregnating the positive electrode body with manganese nitratesolution, a process of natural drying, followed by a process of thermaldecomposition at 300° C.

[0108] It is also possible to form a pre-coating layer having aconductive material such as a conductive polymer or the like in place ofa manganese dioxide layer.

[0109] The solid electrolyte layer having a conductive polymer is formedthrough electrolytic polymerization of a heterocyclic monomer. As aheterocyclic monomer, for example, it is preferable to use a monomersuch as pyrrole, thiophene, aniline, or 3, 4-ethylene dioxythiophene. Byoxidative polymerization of these heterocyclic monomers, it is possibleto relatively easily obtain solid electrolyte layer 4 of conductivepolymer having high conductivity.

[0110] For example, in a polymerizing solution including a heterocyclicmonomer such as pyrrole, applying an electric field thereto from anexternal electrode results in electrolytic polymerization of thepyrrole, thereby forming polypyrrole. In this way, a solid electrolyticcapacitor having excellent characteristics can be reliably obtained in arelatively short period of time.

[0111] Also, the carbon layer may be formed according to the same methodas in the above exemplary embodiment 1.

[0112] Examples in the exemplary embodiment 3 will be described in thefollowing.

EXAMPLE 31

[0113] A surface-roughened aluminum foil increased in surface area byabout 125 times was formed by etching the surface of aluminum foil as anpositive electrode body. An insulative resist tape was affixed to thealuminum foil to separate the aluminum foil into a negative electrodeportion and an positive electrode portion. Immersing the positiveelectrode body of a capacitor element into ammonium dihydrogen phosphatesolution, DC12V was applied to the positive electrode body for 20minutes. The effective area of the positive electrode body is 3.2 mm×3.9mm. The concentration of ammonium dihydrogen phosphate solution is 0.3wt %, and the temperature in the solution is 70° C. Thus, an oxide filmon positive electrode was formed as a dielectric layer.

[0114] Next, the positive electrode body having the oxide film onpositive electrode was immersed into 20 wt % manganese nitrate solutionat 25° C. for 3 seconds, and was taken out thereafter. After that,excess part of the manganese nitrate solution sticking to the surface ofthe positive electrode body having the oxide film on positive electrodewas blown away by air. Subsequently, the positive electrode bodymoistened with manganese nitrate solution was treated at 300° C. for 5minutes, increasing the temperature at a speed of over 250° C. withinone minute. Thus, the manganese nitrate solution was thermallydecomposed and then a solid electrolyte layer of manganese dioxide wasformed on the surface of the dielectric layer.

[0115] Next, the positive electrode body having the dielectric layer andsolid electrolyte layer was immersed in an ammonium dihydrogen phosphatesolution, 3 wt % in concentration and 70° C. in liquid temperature, andthen, DC10V was applied to the positive electrode body for 10 minutes,thereby performing re-formation treatment. Subsequently, a solidelectrolyte layer of conductive polymer of polypyrrole film was formedon the manganese dioxide layer by the above-mentioned electrolyticpolymerization method.

[0116] Next, the surface of the solid electrolyte layer was impregnatedwith alkaline solution containing carbon particles and pyrogallol.Pyrogallol is used as a benzene compound of chemical formula 2. Thealkaline solution contains 5 wt % of carbon particles and 2 wt % ofpyrogallol, and ammonia. The solution is adjusted to pH10 by ammonia.The positive electrode body impregnated with the alkaline solution wasdried at 150° C. In this way, a carbon layer was formed on the surfaceof the solid electrolyte layer. In that case, the carbon layer contains0.2 part by weight of pyrogallol against one part by weight of carbonparticles. After that, a silver paste conductor layer was formed on thesurface of the carbon layer. In this way, a conductor layer on negativeelectrode was formed. Thus, a capacitor element was obtained. A leadwire was led from each of the positive electrode body and the conductorlayer on negative electrode. After that, facing resin is disposed so asto cover the capacitor element. Thus, a solid electrolytic capacitorhaving a shape of 7.3 mm×4.3 mm×2.8 mm in dimension was manufactured.

EXAMPLE 32

[0117] In this example 32, a carbon layer is formed by using alkalinesolution of pH10 which contains 5 wt % of carbon particles and 9 wt % ofpyrogallol. In this case, the carbon layer contained one part by weightof carbon particles and 1.8 part by weight of pyrogallol. The otherconfigurations to obtain a solid electrolytic capacitor are the same asin the above example 31.

Comparative example 4

[0118] In this comparative example 4, a carbon layer is formed by usingalkaline solution of pH10 which contains 5 wt % of carbon particles.That is, the alkaline solution does not contain a benzene compound shownby the chemical formula 1. The other configurations to obtain a solidelectrolytic capacitor are the same as in the above example 31.

[0119] With respect to the solid electrolytic capacitors thus obtainedin the examples 31, 32 and the comparative example 4, the initialcharacteristics (electrostatic capacity “C”, equivalent seriesresistance “ESR”, leak current “LC”), capacity change rate “ΔC” and ESRchange rate “ΔESR” after 1,000 hours of leaving at 105° C. are shown inTable 1. These performances were measured at temperatures of 25 to 30°C. The electrostatic capacity was measured at 120 Hz. ESR was measuredat 100 kHz. As the leak current, the current value was measured 30seconds after applying the rated voltage. Each of the measured values isshown by averaging n=30 specimens. The rating of the solid electrolyticcapacitor is 6.3WV, 22 μF. TABLE 3 Initial values After 1,000 hours C(μF) ESR (mΩ) LC (μA) ΔC (%) ΔESR (%) Example 31 22 25 78 −1.5 5.5Example 32 24 28 78 −1.1 5.3 Comparative 21 32 80 −5.1 21 example 4

[0120] As shown in Table 3, the solid electrolytic capacitors in theexample 31 and the example 32, containing carbon particles andpyrogallol or catechel in the carbon layer, have better initialcharacteristics than those in the comparative example 4. Further, thesolid electrolytic capacitors in the present examples maintain excellentperformance even after 1,000 hours of leaving at high temperatures. Thatis, in the present examples, the electrostatic capacity is 22-24 μF, ESRis 25-28 mΩ, and leak current is 78 μA. Also, after 1,000 hours ofleaving at 105° C., the capacity change rate (ΔC) is 1.1-1.5%, and ESRchange rate is 5.3-5.5%. On the other hand, in the comparative example4, the electrostatic capacity is 21 μF, ESR is 32 mΩ or less, and leakcurrent is 80 μA. Furthermore, after 1,000 hours of leaving at 105° C.,the capacity change rate (ΔC) is 5.1%, and ESR change rate is 21%.

[0121] Thus, the solid electrolytic capacitors in the present examples31 and 32 have better initial characteristics than those in thecomparative example. Further, the capacity change rate and ESR changerate after 1,000 hours of leaving at 105° C. are smaller than those inthe comparative example. Particularly, with respect to the capacitychange rate and ESR change rate after 1,000 hours of leaving at 105° C.,the solid electrolytic capacitors in the present examples are smallerthan those in the comparative example.

[0122] As described above, due to the configuration of the presentinvention, the carbon layer obtained is fine and uniform. Accordingly,the contact resistance between the solid electrolyte layer and thecarbon layer is reduced, and the contact resistance between the carbonlayer and the conductor layer is also reduced. As s result, it ispossible to obtain a solid electrolytic capacitor assuring excellentequivalent series resistance (ESR characteristics) and capacityutilization factor.

What is claimed is:
 1. A solid electrolytic capacitor, comprising: anpositive electrode body; a dielectric layer formed on the surface ofsaid positive electrode body; a solid electrolyte layer formed on thesurface of said dielectric layer; a negative electrode layer disposed onthe surface of said solid electrolyte layer; an positive electrodeterminal electrically connected to said positive electrode body; and anegative electrode terminal electrically connected to said negativeelectrode layer, wherein said negative electrode layer includes a carbonlayer, and said carbon layer contains carbon particles, and a benzenecompound represented by chemical formula 1, where each of R1, R2, R3,and R4 has H, OH group, COOH group, or alkyl group.


2. The solid electrolytic capacitor as defined in claim 1, wherein saidpositive electrode body includes valve metal, and said dielectric layerincludes a dielectric oxide film formed by oxidation of said valvemetal.
 3. The solid electrolytic capacitor as defined in claim 1,wherein said negative electrode layer further includes a conductorlayer, said carbon layer is disposed on the surface of said dielectriclayer, and said conductor layer is disposed on the surface of saidcarbon layer.
 4. The solid electrolytic capacitor as defined in claim 1,wherein said positive electrode body includes valve metal; saiddielectric layer includes a dielectric oxide film formed by oxidation ofsaid valve metal; said negative electrode layer further includes aconductor layer; said carbon layer is disposed on the surface of saiddielectric oxide film; and said conductor layer is disposed on thesurface of said carbon layer.
 5. The solid electrolytic capacitor asdefined in claim 1, further comprising facing resin, wherein said facingresin is disposed so as to cover said positive electrode body, saidsolid electrolyte layer, and said negative electrode layer, in a statesuch that each of said positive electrode terminal and said negativeelectrode terminal is partially exposed from the facing resin.
 6. Thesolid electrolytic capacitor as defined in claim 1, further comprisingfacing resin, wherein said positive electrode body includes valve metal;said dielectric layer includes a dielectric oxide film; said negativeelectrode layer further includes a conductor layer; said carbon layer isdisposed on the surface of said dielectric oxide film; said conductorlayer is disposed on the surface of said carbon layer; and in a statesuch that each of said positive electrode terminal and said negativeelectrode terminal is partially disposed, said facing resin is disposedso as to cover said positive electrode body, said solid electrolytelayer and said negative electrode layer.
 7. The solid electrolyticcapacitor as defined in claim 1, wherein said carbon layer contains onepart by weight of said carbon particles and 0.1 part to 1.8 part byweight of said benzene compound.
 8. The solid electrolytic capacitor asdefined in claim 1, wherein said benzene compound contains at least oneof catechol and pyrogallol.
 9. The solid electrolytic capacitor asdefined in claim 1, wherein said solid electrolyte layer containsmanganese dioxide.
 10. The solid electrolytic capacitor as defined inclaim 1, wherein said solid electrolyte layer includes a conductivepolymer formed of at least one heterocyclic monomer selected from thegroup consisting of pyrrole, thiophene, aniline, and 3, 4-ethylenedioxythiophene.
 11. The solid electrolytic capacitor as defined in claim1, wherein said positive electrode body is formed of at least one of(i)valve metal having a roughened surface and (ii)valve metal sinteredinto porous metal.
 12. The solid electrolytic capacitor as defined inclaim 1, wherein said positive electrode body includes aluminum having aroughened surface, said dielectric layer includes a dielectric oxidefilm formed by surface oxidation of said aluminum.
 13. A solidelectrolytic capacitor, comprising: an positive electrode body formed ofvalve metal; a dielectric oxide film disposed on the surface of saidpositive electrode body; a solid electrolyte layer disposed on thesurface of said dielectric oxide film; a negative electrode layerdisposed on the surface of said solid electrolyte layer; an positiveelectrode terminal electrically connected to said positive electrodebody; a negative electrode terminal electrically connected to saidnegative electrode layer; and facing resin disposed in a state such thateach of said positive electrode terminal and said negative electrodeterminal is partially exposed, wherein said negative electrode layerincludes a carbon layer, and said carbon layer contains carbon particlesand a benzene compound represented by the chemical formula 1, where eachof R1, R2, R3, and R4 has H, OH group, COOH group, or alkyl group.


14. A method for manufacturing a solid electrolytic capacitor,comprising the steps of: (a) forming an positive electrode body; (b)forming a dielectric layer on the surf ace of said positive electrodebody; (c) forming a solid electrolyte layer on the surf ace of saiddielectric layer; (d) forming a negative electrode layer on the surfaceof said solid electrolyte layer, wherein said negative electrode layerincludes a carbon layer, and said carbon layer includes carbon particlesand a benzene compound represented by the chemical formula 1; (e)electrically connecting an positive electrode terminal to said positiveelectrode body; (f) electrically connecting a negative electrodeterminal to said negative electrode layer; and (g) disposing facingresin which covers said positive electrode body, said dielectric layer,said solid electrolyte layer, and said negative electrode layer, whereeach of R1, R2, R3, and R4 has H, OH group, COOH group, or alkyl group.


15. The method for manufacturing a solid electrolytic capacitor asdefined in claim 14, wherein the step of forming said positive electrodebody includes a step of sintering valve metal into porous metal, and thestep of forming said dielectric layer includes a step of forming adielectric oxide film through oxidation of the surface of said valvemetal.
 16. The method for manufacturing a solid electrolytic capacitoras defined in claim 14, wherein the step of forming said negativeelectrode layer includes the steps of disposing the carbon layer, anddisposing a conductor layer on the surface of said carbon layer.
 17. Themethod for manufacturing a solid electrolytic capacitor as defined inclaim 16, wherein the step of forming said conductor layer includes astep of disposing silver paste.
 18. The method for manufacturing a solidelectrolytic capacitor as defined in claim 14, wherein the step offorming said positive electrode body includes at least one of (i)a stepof sintering valve metal into porous metal and (ii)a step of rougheningthe surface of valve metal.
 19. The method for manufacturing a solidelectrolytic capacitor as defined in claim 14, wherein the step offorming said positive electrode body includes at least one of (i)a stepof sintering valve metal into porous metal and (ii)a step of rougheningthe surface of valve metal; the step of forming said dielectric layerincludes a step of forming a dielectric oxide film on the surface ofsaid valve metal; the step of forming said negative electrode layerincludes a step of disposing the carbon layer and a step of disposing aconductive layer having silver paste on the surface of said carbonlayer; and each of said positive electrode terminal and said negativeelectrode terminal is partially disposed at the surface of said facingresin.
 20. The method for manufacturing a solid electrolytic capacitoras defined in claim 14, wherein said carton layer contains one part byweight of carbon particles and 0.1 part to 1.8 part by weight of saidbenzene compound.
 21. The method for manufacturing a solid electrolyticcapacitor as defined in claim 14, wherein said benzene compound containsat least one of catechol and pyrogallol.
 22. The method formanufacturing a solid electrolytic capacitor as defined in claim 14,wherein the step of forming said carbon layer includes a step ofapplying a mixture containing carbon particles, a benzene compoundrepresented by the chemical formula 1 and liquid to said solidelectrolyte, and a step of removing the liquid.
 23. The method formanufacturing a solid electrolytic capacitor as defined in claim 14,wherein the step of forming said carbon layer includes the steps ofpreparing a suspension containing carbon particles and liquid; preparinga mixed suspension by dissolving a benzene compound represented by thechemical formula 1 in said suspension; immersing said positive electrodebody having said solid electrolyte layer into said mixed suspension;taking said positive electrode body having said solid electrolyte layermoistened with said mixed suspension out of said mixed suspension; anddrying said positive electrode body having said solid electrolyte layermoistened with said mixed suspension.
 24. The method for manufacturing asolid electrolytic capacitor as defined in claim 22, wherein saidmixture is a suspension that has been alkalized.
 25. The method formanufacturing a solid electrolytic capacitor as defined in claim 22,wherein said carbon particles are contained in said mixture in a rangefrom 2 wt % to 10 wt %.
 26. The method for manufacturing a solidelectrolytic capacitor as defined in claim 14, wherein the step offorming said solid electrolyte layer includes at least one of (i) a stepof forming manganese dioxide, and (ii) a step of forming a conductivepolymer by polymerization of a hetercyclic monomer.
 27. The method formanufacturing a solid electrolytic capacitor as defined in claim 14,wherein the step of forming said solid electrolyte layer includes a stepof forming a conductive polymer through polymerization of at least oneheterocyclic monomer selected from the group consisting of pyrrole,thiophene, aniline, and 3, 4-ethylene dioxythiophene.
 28. The method formanufacturing a solid electrolytic capacitor as defined in claim 14,wherein the step of said solid electrolyte layer includes a process offorming a conductive polymer layer, and the step of forming saidconductive polymer layer includes at least one selected from the groupconsisting of (i) (a) a step of impregnating the surface of saiddielectric layer, formed on the surface of said positive electrode body,with a polymerizing solution containing a heterocylic monomer, furtherimpregnating same with an oxidizing solution containing an oxidizingagent, followed by cleaning and recovery formation; and (b) a step ofrepeating the step (a) by a plurality of times; and (ii) (c) a step ofimpregnating the surface of said dielectric layer, formed on the surfaceof said positive electrode body, with a mixed solution containing aheterocyclic monomer and an oxidizing agent; and (d) a step of repeatingthe step (c) by a plurality of times; and (iii) (e) a step ofimpregnating the surface of said dielectric layer, formed on the surfaceof said positive electrode body, with a polymerizing solution containinga heterocyclic monomer, further impregnating same with an oxidizingsolution containing an oxidizing agent and also with a mixed solutioncontaining a heterocyclic monomer and an oxidizing agent, followed bycleaning and recovery formation; and (f) a step of repeating the step(e) by a plurality of times.
 29. A method for manufacturing a solidelectrolytic capacitor, comprising the steps of: (a) forming an positiveelectrode body having valve metal sintered into porous metal; (b)forming a dielectric layer on the surface of said positive electrodebody; (c) forming a solid electrolyte layer on the surface of saiddielectric layer; (d) forming a negative electrode layer on the surfaceof said solid electrolyte layer, wherein said negative electrode layerincludes a carbon layer, and a silver paste layer as a conductor layer,and said carbon layer contains carbon particles and a benzene compoundshown by the chemical formula 1; (e) electrically connecting an positiveelectrode terminal to said positive electrode body; (f) electricallyconnecting a negative electrode terminal to said negative electrodelayer; and (g) disposing facing resin so as to cover said positiveelectrode body, said dielectric layer, said solid electrolyte layer, andsaid negative electrode layer, where each of R1, R2, R3, and R4 has H,OH group, COOH group, or alkyl group.